Fig. 3.

Delayed erythropoiesis and megakaryopoiesis in scat spleen. (A) An increase in total spleen cell number (Left) attributable to a dramatic increase in Ter119⁺ erythroid cells (Center) is seen in the scat crisis spleen. All values X ± SEM; *P < 0.05, t test. (B) By flow cytometry using CD44 and Ter119 or CD44 and forward scatter (FSC) as markers of differentiation, a significant block in erythropoiesis is observed in scat during crisis. (C and D) Quantitation of the different spleen populations demonstrates an accumulation of polychromatophilic and orthochromatic erythroblasts (C) associated with a decrease in hemoglobinization within these cells (D). X ± SEM; *P < 0.05, t test. (E) An increased number of megakaryocytes is seen during crisis as evidenced by acetylcholinesterase staining. (F) By transmission electron microscopy, scat crisis megakaryocytes display features characteristic of a significant developmental delay. See text for details. During remission, megakaryocyte characteristics normalize.